The present invention relates generally to electromagnetic energy collection and more particularly to devices useful in the collection and utilization of radiant energy from solar and other sources.
The prior art has proposed numerous devices for detection of electromagnetic energy (e.g., infrared scanners, detectors of light from high energy particles, and the like) and for collection of such energy (e.g., microwave antennas, solar collectors, and the like) and is particularly rich in suggestions of systems for collection and utilization of solar energy.
Notwithstanding the voluminous proposals of the art, among the basic, and as yet inadequately resolved, problems inherent in the efficient utilization of solar energy are avoidance of energy loss through re-radiation (i.e., energy conservation) and avoidance of intricate, and hence costly, apparatus for tracking the sun in its apparent daily motion through the celestial sphere.
A typical attempt to solve solar energy conservation problems involves providing selective coatings on energy absorbing surfaces as well as elaborate insulation of the particular "trap" employed for the utilization of collected energy. U.S. Pat. No. 3,277,884, for example, illustrates such a scheme.
Another common manner of dealing with energy conservation involves including in the collection scheme reflective or refractive concentration apparatus to permit collection of solar energy impinging upon a relatively large area and focusing of collected energy toward a relatively small area of utilization. Typical schemes proposing use of reflector concentrators are illustrated in U.S. Pat. Nos. 1,814,897, 3,200,820 and 3,217,702, for example. ("Shadowing" effects encountered in disposing an energy utilization body in path of sunlight impinging upon reflectors are to some extent avoided through use of off-axis reflectors, as in U.S. Pat. Nos. 3,052,229, 3,613,659 and Tabor, "Stationary Mirror Systems for Solar Collectors" Solar Energy, Vol. II, No. 3-4, pp. 27 et seq. (1958)). Typical lens systems for solar concentration are illustrated in U.S. Pat. No. 3,125,091 and Meinel et al., "Physics Looks at Solar Energy" Physics Today, Vol. 25, pp. 684 et seq. (1972). All of the mirroring and lens systems proposed above are basically imaging systems wherein solar energy is reflected or refracted to a system focal point at which the "concentrated" energy is utilized for heating or power generation.
Among the solutions proposed for avoidance of diurnal solar tracking is the provision of huge, but marginally efficient, mirrored surfaces such as shown in U.S. Pat. No. 3,179,105.
None of the prior art systems has adequately solved the problems of energy conservation and solar tracking and, to a degree, solution of one problem often tends to enlarge the difficulties posed by the other. This is to say that systems permitting solar concentration by large factors generally will require the most careful and frequent diurnal adjustments for solar tracking. Conversely, systems requiring little or no diurnal adjustment generally provide lowest factors of concentration. Thus, Tabor, infra concludes that the maximum concentration available in a stationary system (i.e., one requiring only seasonal tracking) is on the order of 3 or 4.
Non-imaging light funnels having utility in collection of light from high energy particles and having a greater concentration capacity than imaging systems have been proposed by the inventor and his collaborators in earlier publications, i.e., Review of Scientific Instruments, Vol. 37, No. 8, pp. 1094-5 (1966), ibid., Vol. 39, No. 3, pp. 419-20 (1968), ibid., Vol. 39, No. 8, pp. 1217-8 (1968), and J. Opt. Soc. Am., Vol. 60, No. 2, pp. 245-7 (1970). The inventor also noted the similarity between such funnels and the geometry of retinal cones in J. Opt. Soc. Am., Vol. 61, No. 8, pp. 1120-1 (1971). Basically, the above publications dealt with proposals for "ideal", conical-shaped, light collectors which approach an f number equal to 0.5, a physically unrealizable limit for lens systems. The field of acceptance of conical collectors therein proposed may be represented by a right circular cone having a gradually diminishing (over about 1.degree.) external boundary cut-off.